To accept this offer, you must first cancel the auction to remove your asset from the auction contract.Keep this tab open. Once complete, you will be able to click "Accept Offer" again to execute the transaction.
BRAVE FRONTIER HEROES will use Ethereum to manage the ownership of the game assets. Units (Character) and Spheres (Equipment) are ERC-721 tokens. You can get digital assets by quests or as a reward of PvP events. Of course, they can be traded in marketplace like OpenSea.